In general, an ignition apparatus used for an ignition plug such as a plasma jet ignition plug includes a power supply which applies a voltage to a gap formed between a center electrode and a ground electrode of the ignition plug to thereby generate a spark discharge, and a power supply for supplying electric power to the gap. Also, a connection device for connecting the two power supplies to the ignition plug has a first power supply side line which establishes connection between the ignition plug and the power supply (first power supply) for supplying electric power to the gap, and a second power supply side line which establishes connection between the ignition plug and the power supply (second power supply) for applying a voltage to the gap. A diode is provided between the ignition plug and the first power supply, and another diode is provided between the ignition plug and the second power supply, to thereby prevent a current flow from one of the first and second power supplies into the other of the first and second power supplies (see, for example, Patent Document 1, etc.).
Incidentally, in an ignition apparatus as described above, a large current flows into the ignition plug immediately after generation of spark discharge, and electromagnetic wave noise may be generated. This phenomenon occurs because charges stored in stray capacitances present between the ignition plug and the two diodes instantaneously flow to the gap immediately after generation of spark discharge while hardly being restrained by the resistance components of the lines. A method for restraining generation of such noise has been proposed (see, for example, Patent Document 2, etc.). In the proposed method, a resistor is provided between the ignition plug and the second power supply, the resistor is disposed as close as possible to the center electrode of the ignition plug, and the diode provided between the ignition plug and the first power supply is disposed as close as possible to the center electrode, to thereby minimize the length of the wiring between the ignition plug and the resistor and the length of the wiring between the ignition plug and the diode on the first power supply side. This method can reduce the stray capacitance between the ignition plug and the resistor and the stray capacitance between the ignition plug and the diode on the first power supply side (in other words, charges which instantaneously flow to the gap without being restrained by the resistance components), whereby noise can be suppressed.